Why You Must Apply Sunscreen Before the Beach

Plus, 6 other sunscreen mistakes that can set you up for a serious burn

Okay, so you are ahead of the curve if you actually bought a bottle of sunscreen and aim to slather some on this summer. But even if your intentions are good, your execution might leave something to be desired.

In fact, people generally make a bunch of mistakes when applying sunscreen, researchers reported in the Journal of the American Academy of Dermatology. And each little mistake you make before you head out in the rays leaves your skin vulnerable to a nasty burn, which can up your risk of skin cancer—including deadly melanoma—down the line.

Here, seven of the most common sunscreen snafus people make—and how you can avoid falling victim to the same fate.

The sun emits UVA and UVB rays—and both have the potential to damage your skin.

So you want a sunscreen that blocks both of them. Thankfully, there’s an easy way to make sure: Simply look for the word “broad-spectrum” on the bottle, says Heather Rogers, M.D., clinical assistant professor of dermatology at the University of Washington.

Blocking both is vital to your skin’s health. UVA rays are associated with wrinkling, dark spots, and aging of your skin, while UVB rays are the ones that cause sunburn and are most associated with skin cancer.

The U.S. Food and Drug Administration (FDA) regulates sunscreen, and has approved 16 active ingredients for sun protection. But if you have sensitive skin, you may want use mineral-based sunscreen, which contain titanium dioxide or zinc oxide. These active mineral ingredients are less likely than the ingredients in chemical-based sunscreens—like oxybenzone, avobenzone, octisalate, and octinoxate—to cause an allergic reaction, which can irritate your skin, says Dr. Rogers.

Being inside doesn’t protect you 100 percent. Windows block out UVB rays, but UVA rays can still pass through.

“UVA rays have the longest wavelength,” says Dr. Rogers. “They don’t cause sunburn, but they penetrate deep into the skin, causing dark spots and wrinkles.” (Here's how to become better looking as you age.)

But they may play a role in skin cancer, too: Seventy-four percent of malignant melanomas in men occur on the left side of the body—the side exposed to sunlight while driving, according to a study in the Journal of the American Academy of Dermatology.

It’s the side windows that raise your risk the most: According to a study in JAMA Ophthalmology, front windshields block out an average of 96 percent of the UV rays—comparable to an SPF of 30. Side windows, on the other hand, blocked only 71 percent on average. So that can add up to some serious damage.

The gloom and gray of an overcast day might give you a false sense of safety. If you can’t see the sun, it’s probably not hurting you, right? Wrong. Clouds definitely dampen the strength of the sun’s rays, but they don’t kill them off completely.

And you have to be extra vigilant in the summer—that’s when the sun rises higher in the sky and it hits us at a more perpendicular angle, causing more direct rays than those we get in winter, Dr. Gohara says.

So if you’re outside and unprotected, regardless of whether the sun’s unobstructed, your skin might pay the price.

“As long as you can see your hand in front of your face, there are enough ultraviolet rays out to cause skin cancer and aging,” says Mona Gohara, M.D., a dermatologist and associate clinical professor in the Department of Dermatology at Yale University. Slather up no matter how overcast the sky.

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SUNSCREEN MISTAKE: Applying too little, too late

“Sunscreen is only as good as the job you do applying it,” Dr. Rogers says.

For full coverage, try portioning out your sunscreen for each section of your body—you should total about the contents of a shot glass, according to the American Academy of Dermatology.

When men portioned out their sunscreen before applying it, they used 51 percent more sunscreen and covered 83 percent more skin, one 2014 study found.

Make sure you apply early enough, too. Mineral sunscreens—which work by reflecting, scattering, and blocking UV rays—don’t need extra time to activate. But chemical sunscreens, known as “chemical absorbers” because they convert UV rays into heat, need 30 minutes to set into your skin.

So if you wait to apply until you’re already at the beach, you’re giving your skin ample time to burn before its protection kicks in.

The often-overlooked bottom lip is much more likely to develop skin cancer than the top one, thanks to its slight pout, which exposes it more to the rays. In fact, about 80 percent of lip cancers occur on the bottom lip, according to a study in the journal Anticancer Research.

Use an SPF 30 lip balm, and don’t forget other vulnerable spots, like your scalp and your ears. These areas tend to develop skin cancers that become more aggressive later in life, Dr. Gohara says.

Dr. Rogers recommends using this guideline: Make sure you’re hitting any area that’s perpendicular to the sun, like the top of your head, shoulders, and tops of your feet, because they get a more direct hit of the rays.

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SUNSCREEN MISTAKE: CONSIDERING IT A ONE-AND-DONE DEAL

So you chose a broad-spectrum bottle and applied an adequate amount of it 30 minutes before you headed outdoors. But you’re not in the clear just yet: Sunscreens won’t last you all day, regardless of SPF.

SPF stands for sun protective factor, and it’s a measure of your protection from the sun. “If you’re wearing an SPF 10 sunscreen, it will take 10 times longer for you to burn than if you’re wearing none,” Dr. Rogers says.

But sunscreens tend to break down once you’re in the sun. So after two hours, you’re not as protected as you once were, she explains.

Apply and reapply: The American Academy of Dermatology recommends using one ounce of sunscreen—again, about enough to fill a shot glass—to cover exposed skin, and reapplying every two hours, or after a swim or sweat session.

In the Journal of the American Academy of Dermatology study, 38 percent of people used sunscreen as their only form of protection. That’s a no-no, especially when you’re out in the middle of the day.

You generally want to avoid being in the sun between 10 a.m. and 4 p.m., Dr. Lin says. That’s when the sun’s rays are strongest—and you are more likely to get burned, even if you did apply sunscreen.

If you must be outdoors in that timeframe, “wear a hat and protective clothing, like long-sleeve shirts with high collars,” he says.

Any old T-shirt won’t do. Protection in clothing is measured by UPF—ultraviolet protection factor—rather than SPF. A plain white tee offers weak protection, with a UPF of about 8 when it’s dry, and 4 when it’s wet, Dr. Rogers says. (That’s why you’re more likely to burn if you pop on your shirt when you’re still soaked from a swim).

“If you’re going to use a shirt as sun protection, it has to be dark in color and a really tight weave.” Invest in some UV-protective clothing and consider washing your wardrobe with a UPF-boosting detergent like Rit SunGuard, which is recommended by the Skin Cancer Foundation. One cycle boosts your clothes’ UPF to 30 for up to 20 washes.

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